1. Field of the Invention
This invention relates to a fuel injection control system for use with an internal combustion engine and, more particularly, to a system for cutting off the supply of fuel to the engine during engine deceleration.
2. Description of the Prior Art
Electronic controlled fuel injection systems have already been proposed which include a fuel cut-off device for cutting off the supply of fuel to an internal combustion engine when the throttle valve is fully closed and the engine speed is above a predetemined reference value for fuel economy during engine deceleration.
With such conventional systems, however, any attempt to lower the reference engine speed value so as to provide a wider fuel cut-off range for higher fuel economy, would lead to a sudden engine speed drop at the start of fuel cut-off and a sudden output torque change resulting in a vehicle shock upon fuel supply resumption. This is due to a time lag between an engine speed detection and an actual engine output torque appearance.
In order to suppress any sudden engine speed drop as well as achieve higher fuel economy, improved systems have also been proposed which are adapted to cut off the supply of fuel to some of the cylinders when the engine speed is above a first predetermined value during engine deceleration and cut off the supply of fuel to the remaining cylinders when the engine speed is above a second predetermined value higher than the first predetermined value during engine deceleration. However, such conventional systems have been found unsatisfactory in that when a rapid engine deceleration occurs, for example, just after engine racing, a sudden large engine speed drop appears which would result in engine stalling.
The present invention provides means responsive to rapid engine deceleration for temporarily increasing the lower predetermined engine speed reference value to resume the supply of fuel to all of the cylinders of an engine at a higher engine speed.